Check out grounddynamics.com. They have conversions from $300-$4000, and will beat any advertised price. There JDM Type-R is my favorite. But converting it from 4dr to 2dr would require a lot of cutting and such, so it would cost a lot. I would just leave it as is, besides 4 doors are more convenient anyway. And as far as other upgrades, I would suggest a Greddy turbo kit from greddy.com. And beef up the suspension to make it fun to drive.